Mean Opinion Score (MOS): MOS is a subjective method that can straightforwardly evaluate perceptual quality. Specifically, a number of viewers rate their opinions on the quality of a set of images by Double-stimulus [1]}, i.e., every viewer has both the source and test images. After all the viewers finishing ratings, the results are mapped onto numerical values and the average scores will be the final MOS. MOS is a time-consuming and expensive method as it requires manual participation. Meanwhile, MOS is also doubted to be unstable, since the MOS differences may be not noticeable to the users. Moreover, this method is too subjective to guarantee fairness.
